Learn How Hackers Can Hijack Your Online Accounts Even Before You Create Them.

Malicious actors can gain unauthorized access to users' online accounts via a new technique called "account pre-hijacking," new research has found.

The attack takes aim at the account creation process that's ubiquitous in websites and other online platforms, enabling an adversary to perform a set of actions before an unsuspecting victim creates an account in a target service.

The study was led by independent security researcher Avinash Sudhodanan in collaboration with Andrew Paverd of the Microsoft Security Response Center (MSRC).

Pre-hijacking banks on the prerequisite that an attacker is already in possession of a unique identifier associated with a victim, such as an email address or phone number, which can be obtained either from the target's social media accounts or credential dumps circulating on the web.

The attacks can then play out in five different ways, including the use of the same email address during account creation by both the adversary and the victim, potentially granting the two parties concurrent access to the account.

"If the attacker can create an account at a target service using the victim's email address before the victim creates an account, the attacker could then use various techniques to put the account into a pre-hijacked state," the researchers said.

account pre-hijacking

"After the victim has recovered access and started using the account, the attacker could regain access and take over the account." The five types of pre-hijacking attacks are below -

Classic-Federated Merge Attack, in which two accounts created using classic and federated identity routes with the same email address allow the victim and the attacker to access to the same account.

Unexpired Session Identifier Attack, in which the attacker creates an account using the victim's email address and maintains a long-running active session. When the user recovers the account using the same email address, the attacker continues to maintain access because the password reset did not terminate the attacker's session.

Trojan Identifier Attack, in which the attacker creates an account using the victim's email address and then adds a trojan identifier, say, a secondary email address or a phone number under their control. Thus when the actual user recovers access following a password reset, the attacker can use the trojan identifier to regain access to the account.

Unexpired Email Change Attack, in which the attacker creates an account using the victim's email address and proceeds to change the email address to one under their control. When the service sends a verification URL to the new email address, the attacker waits for the victim to recover and start using the account before completing the change-of-email process to seize control of the account.

Non-Verifying Identity Provider (IdP) Attack, in which the attacker creates an account with the target service using a non-verifying IdP. If the victim creates an account using the classic registration method with the same email address, it enables the attacker to gain access to the account.

In an empirical evaluation of 75 of the most popular websites from Alexa, 56 pre-hijacking vulnerabilities were identified on 35 services. This includes 13 Classic-Federated Merge, 19 Unexpired Session Identifier, 12 Trojan Identifier, 11 Unexpired Email Change, and one Non-Verifying IdP attacks -

Dropbox - Unexpired Email Change Attack

Instagram - Trojan Identifier Attack

LinkedIn - Unexpired Session and Trojan Identifier Attacks

Wordpress.com - Unexpired Session and Unexpired Email Change Attacks, and

Zoom - Classic-Federated Merge and Non-verifying IdP Attacks

"The root cause of all of the attacks [...] is a failure to verify ownership of the claimed identifier," the researchers said.

"Although many services do perform this type of verification, they often do so asynchronously, allowing the user to use certain features of the account before the identifier has been verified. Although this might improve usability (reduces user friction during sign up), it leaves the user vulnerable to pre-hijacking attacks."

account pre-hijacking

While implementing strict identifier verification in services is crucial to mitigating pre-hijacking attacks, it's recommended that users secure their accounts with multi-factor authentication (MFA).

"Correctly implemented MFA will prevent the attacker from authenticating to a pre-hijacked account after the victim starts using this account," the researchers noted. "The service must also invalidate any sessions created prior to the activation of MFA to prevent the Unexpired Session attack."

On top of that, online services are also advised to periodically delete unverified accounts, enforce a low window to confirm a change of email address, and invalidate sessions during password resets for a defense in-depth approach to account management.

"When a service merges an account created via the classic route with one created via the federated route (or vice-versa), the service must ensure that the user currently controls both accounts," Sudhodanan and Paverd said.

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